U---Pb, Sr and Nd evidence for grenvillian and latest proterozoic tectonothermal activity in the spitsbergen caledonides, arctic ocean

Within the Caledonian complexes of northwestern Spitsbergen, high PT formations provide U---Pb zircon ages of 965±1 Ma of a metagranite and 955±1 Ma of a corona gabbro, indicating the influence of Grenvillian activity in the area. Various isotopic systems suggest that these rocks were partially derived by reworking of ancient crust (as old as Archaean). Eclogites and felsic agmatite indicate latest Proterozoic magmatic or metamorphic events (625₋₅⁺² and 661±2 Ma, respectively) by U---Pb zircon dating. The eclogitic metamorphism age is not fully constrained and ranges between 540 and 620 Ma; this occurred prior to the superimposed Caledonian metamorphism, indicated by a part of the K---Ar and Rb---Sr mineral cooling ages. The new data and other evidence of Precambrian tectonothermal activity on Svalbard suggest that the Early Palaeozoic and Late Proterozoic successions exposed elsewhere on Svalbard may also be underlain by Grenvillian or older basement rocks. Relationships to other Grenvillian and older terrains in the Arctic are reviewed.